Developing liquid recovery device in a copying machine

ABSTRACT

In a copying machine, especially of the liquid development type, a developing liquid recovery device includes heating means for heating wet-developed copy mediums to dry and fix them with developing liquid vapor produced from the copy mediums. Condenser means is provided for cooling the developing liquid vapor by means of a heat exchanger to thereby form the vapor into mist. Mist collector means for electrically charging the mist-like developing liquid vapor collects the vapor in an electric field. Circulating means is provided for circulating an air flow through the heating means, the condenser means and the mist collector means in succession.

United States Patent n Katayama et al.

[ 1 DEVELOPING LIQUID RECOVERY DEVICE IN A COPYING MACHINE [75]Inventors: Hajime Katayama; Koichi Miyamoto, both of Tokyo; ShojiOhashi, Yokohama, all of Japan {73] Assignee: Canon Kabushiki Kaisha,Tokyo,

Japan [22] Filed: Dec. 19, 1973 [21] Appl. No.: 426,054

[56] References Cited UNITED STATES PATENTS 2,181 ,672 11/1939 Sutclilfcct a1 34/73 2,367,487 l/1945 Desetti et a1 r 1 A 34/77 2,486,877 11/1949Ramsburg ct a1 118/628 1 June 24, 1975 2,554,109 5/1951 Longhurst 34/732,856,848 10/1958 Pritchard 118/628 3,046,936 7/1962 Simons, Jr. A.118/628 3,071,866 1/1963 Mangus r 34/73 3,087,254 4/1963 Kueodera 34/773.1 16,625 1/1964 Stewart... A. 34/77 3,140,159 7/1964 Carlson r r 34/233,199,223 8/1965 Carlson 34/77 3,468,604 9/1969 Matkovich et a1 355/103,637,976 l/l972 Ohta et al. 219/216 Primary Examinerlohn J. CambyAssistant Examiner-Henry C. Yuen Attorney, Agent, or FirmFitzpatrick,Cella, Harper & Scinto [57] ABSTRACT In a copying machine, especially ofthe liquid develop ment type, a developing liquid recovery deviceincludes heating means for heating wet-developed copy mediums to dry andfix them with developing liquid vapor produced from the copy mediums.Condenser means is provided for cooling the developing liquid vapor bymeans of a heat exchanger to thereby form the vapor into mist. Mistcollector means for electrically charging the mist-like developingliquid vapor collects the vapor in an electric field Circulating meansis provided for circulating an air flow through the heating means, thecondenser means and the mist collector means in succession.

12 Claims, 8 Drawing Figures PAIENTED JUN 24 ms SHEET PATENTEDJUH24 1915SHEET PATENTEDJUM 24 ms SHEET FIG. 4

l DEVELOPING LIQUID RECOVERY DEVICE IN A COPYING MACHINE BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates to adeveloping liquid recovery device for use in a copying machine. Moreparticularly, it relates to a carrier liquid recovery device for use inan electrophotographic copying machine of the wet development type.

2. Description of the Prior Art In an electrophotographic copyingmachine of the wet development type, it has usually been the practice toform an electrostatic latent image on a photosensitive sheet or mediumas by the application of electrostatic charge and image light, directthe image-bearing sheet or medium into a pool of developing liquidcomposed of carrier liquid such as Isopar or like petroleum with tonerdispersed therein and develop the latent image into a visible image.When a photosensitive sheet is used, most of the developing liquidremaining thereon is then squeezed by a pair of squeeze roller,whereafter any residual carrier liquid on the photosensitive sheet isvaporized by a fixing-drying device to fix the toner on the sheet. Incase of an image transfer type copier, the toner image on thephotosensitive medium is transferred to a transfer medium through theagency of carrier liquid, and such transfer medium is further passed toa fixing-drying device, where the residual carrier liquid is vaporizedto fix the toner image.

The carrier vapor produced in the above case is usually exhausted fromthe machine directly into the atomosphere such as office room or thelike, but any slight amount of carrier liquid should not be neglectedbecause it is a hygienically deleterious petroleum solvent. Especially,if a copying machine were installed in a shut-up room, the carrier vaporexhausted from the machine at a high rate per unit time would harm thehealth of the workers in the room inasmuch as the rate of exhaust isnowadays in the tendency toward further increase with the increasingcopying speed.

Also, the amount of the carrier liquid carried away with thephotosensitive sheet or the transfer sheet from the developing device isinappreciable when taken with respect to an individual sheet (0.3 to 1cc per sheet of format A), whereas mass production of copies wouldinvolve a considerable waste of carrier liquid which should never beneglected from an economical point of view.

Recovery of carrier vapor by utilizing the adsorbing property of activecarbon or by condensing the vapor has heretofore been proposed, but itis nearly impossible to attain sufficient recovery of carrier vapor bythese means.

Recovery of carrier vapor by cooling and condensing the vapor has alsobeen proposed. However, the recovered carrier liquid is heated to a hightemperature in the fixing station to dry and fix the copy medium. As aresult, part of the carrier liquid is thermally cracked and activated,thus producing a considerably unpleasant odor. If such odorous carrierliquid were returned to the developing liquid for repeated use, the odorwould remain on copy mediums even after they have passed through thefixing-drying device, and such residual odor would finally be exhaustedwith copy mediums to give unpleasantness to the workers in the room,although the odor might be slight in extent.

SUMMARY OF THE INVENTION It is an object of the present invention toprevent exhaust air contaminated by the vapor of developing liquid,especially carrier liquid in an electrophotographic copying machine ofthe wet development type from being discharged outwardly of the machine,and to recover the developing liquid efficiently.

It is another object of the present invention to enable the carriervapor to be cyclically used without being discharged outwardly of themachine and to cause the carrier vapor to be condensed to a high densityin a circulating system and recovered from the air to thereby eliminatethe hygienic problem while, at the same time, to permit the recoveredcarrier liquid to be reused for development, thereby providing aneconomical advantage as well.

It is still another object of the present invention to provide a devicewhich can separate the recovered carrier liquid from the water containedin the air and copy mediums and recirculate the carrier liquid aloneinto the developing tank for reuse.

It is yet another object of the present invention to provide a device inan electrophotographic copying machine having a carrier liquid recoverydevice, which device can deodor and decolor the recovered carrier liquidto make such liquid effective for reuse.

It is a further object of the present invention to enable the carriervapor to be cyclically used without being discharged outwardly of themachine and to cause the carrier vapor to be condensed to a high densityin the circulating system for recovery from the air, thereafter to passthe recovered carrier through an adsorbent such as active carbon, silicagel, active alu mina, active magnesium, acid clay, bentonite, diatomite,calcium carbonate, titanium oxide or the like to thereby deodor andpurify the recovered carrier liquid, thus making it ready for reuse fordevelopment.

The developing liquid recovery device of the present invention comprisesa fixing-drying chamber hermetically sealed as far as possible exceptfor the inlet and outlet ports for copy paper so that the air in thechamber may be recirculated by a blower so as to be repeatedly used forthe fixing and drying while the interior of the chamber is beingmaintained at a pressure level below the atomospheric pressure tothereby prevent exhaust of the air containing carrier vapor. In the aircirculating system, a carrier vapor recovery device is provided so thatan amount of air corresponding to the amount of air admitted through thegaps of the chamber may be made hygienically harmless and exhaustedoutwardly of the machine. More specifically, the carrier vapor once usedfor the fixing-drying is directed into a condenser and a mist collectorfor recovery of the carrier, whereafter most of the air is directed intothe fixing-drying chamber by a blower for cyclical use, while the restof the air is directed into a cooler to remove most carrier vaportherefrom before it is exhausted from the machine. The condensercomprises a flat, orthogonal flow type heat-exchanger as a first stagein which the low-temperature air subjected to carrier recovery is madeinto a low-temperature fluid, and a flat, orthogonal flow typeheat-exchanger for making ambient air into a low-temperature fluid. Themist collector is designed to collect the mist in an electric field, themist being charged with corona discharge.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofa copying machine which adopts an embodiment of the present invention.

FIG. 2 is a perspective view showing a form of the heat-exchangecondenser means.

FIGS. 3 and 4 are fragmentary perspective views showing two forms of themist collector means.

FIG. 5 shows a tank for recovered carrier liquid and a developingdevice.

FIG. 6 schematically shows liquid level detector means provided in thetank and developing device of FIG. 5.

FIG. 7 is a diagram of the electric circuit in the device of the presentinvention.

FIG. 8 is a circuit diagram of the liquid level detector means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, there isshown an embodiment of the present invention. A transfer paper sheet S,which bears a visual image transferred from a photosensitive sheet ormedium having an electrostatic latent image developed by means ofdeveloping liquid, may be admitted into a fixing-drying chamber 1through an inlet port 2 and discharged therefrom through an outlet port3 into a tray 4. The fixing-drying chamber is hermetically sealed as faras possible with its inlet and outlet ports 2 and 3 being sealinglyclosed by sealing rollers 5 5 and 6,, 6 respectively. When admitted intothe fixing-drying chamber 1 through its inlet port 2, the transfer papersheet S may be moved forward with its back side in intimate contact witha heated plate 7 having a heater contained therein and with itsimagebearing surface exposed to the blast from a duct 8 for preparatorydrying. Subsequently, the sheet S may pass between a heat roller 9having a heater contained therein and a press roller I so as to be driedand fixed with the carrier liquid completely vaporized.

A suction port 1] is provided in the latter half portion of thefixing-drying chamber 1 to direct the hot air with the carrier vaporinto a recovery device 13 provided in a portion of a stand 12 for thecopying machine. The air so directed into the recovery device 13 maythen be passed through a heat-exchange condenser 14 and a mist collectorl and sucked into a blower 16. The air is blown off from the blower l6and possed through a duct 17 and a heat-exchanger 14 into a duct 8,through which the air may again be blown off from the fixingdryingchamber 1. Thus, there is provided a circulation path. Part of the airmay be divisionally directed by a duct 17 into a cooling chamber 18 suchas refrigerator, and then exhausted through an exhaust port 19.

In the above-described arrangement, air with carrier liquid in thefixing-drying chamber 1 is circulated by the blower 16, except for thatpart of the air which is exhaused through the exhaust port 19, so thatthe interior of the fixing-drying chamber 1 is below the atmosphericpressure. This prevents the air containing a high density of carriervapor in the chamber 1 from leaking therefrom through some gaps thepresence of which is actually unavoidable to such chamber. Rather, thechamber sucks a small amount of air thereinto through those gaps. It isan amount of air corresponding to or more than such a small amount ofair that is exhausted through the exhaust port I9.

The recovery of carrier liquid will now be described. The heat-exchangecondenser 14, as is shown in FIG. 2, in an orthogonal flow typeheat-exchanger comprising a plurality of sheets 20 of goodheat-conductivity laminated with spacers 21 interposed therebetween. Thecooling side of the condenser 14 is formed into three stages. The firststage 14 is meant to cool the air down to the room temperature torecover the carrier liquid contained therein, and the air used ascoolant therein is the air flow A3 which is to be returned to thefixing-drying chamber 1. In the second and third stages I4 and 14ambient air flows Cl, C2 and C3 sucked thereinto by a fan 22 (FIG. I)are used as coolant. The hot air flow AI containing a high density ofcarrier vapor directed from the fixing-drying chamber 1 is cooled downto a temperature near the room temperature as it is passed through theabove-described heatexchange condenser I4. As the cooling progresses,the carrier vapor in the air AI is over-saturated so that part of suchvapor is deposited on the walls of the condenser and progressively grownup into large drops of liquid, which finally fall from gravity. Most ofthe rest of the carrier vapor changes into minute particles which remainsuspended as mist in the air. The air A2 containing the carrier mist andso cooled down to a temperature near the room temperature is thendirected to the mist collector 15.

The mist collector 15, as is shown in FIG. 3, comprises electrode plates23 with a high DC voltage applied thereto and earthed electrode platesor meshes 24, the plates 23 and meshes 24 being alternately arranged andsuitably spaced apart for insulation from each other. Each electrodeplate 23 has a needle discharge electrode 25 provided adjacent theentrance of the collector.

The mist suspended in the air A3 is passed through the corona dischargebetween each needle electrode and adjacent earthed electrode, wherebythe mist is electrically charged. When passing through the subsequentfield between the electrodes, the charged mist is attracted to theearthed electrode by Coulomb force and deposited thereon, so that thecharged mist is neutralized for dripping. If the earthed electrode werein the form of wall (FIG. 3), the entire wall surface of the earthedelectrode would be covered with carrier liquid too rapidly for thecharged mist to be well neutralized.

More particularly, the charged mist loses its charge after it has beendeposited on the earthed electrode, and the speed at which the chargedmist loses its charge is variable depending on the magnitude of theelectrical resistance of the mist itself. If the entire wall surface ofthe earthed or ground electrode is covered up with carrier liquid. theapparent electrical resistance of the charged mist will become highereven though the mist reaches the wall surface due to Coulomb force, thusreducing the speed at which the mist loses its charge (i.e. the speed atwhich the mist is neutralized). Moreover, as a greater deal of chargedmist gathers with the progress of continuous copying, the quantity ofcharged mist overcomes the speed at which the charge is lost, and thusmore and more of charged mist gathers there until it results in sparkdischarge. For this reason, the neutralization of charged mist mustproceed at an appropriate speed.

On the other hand, on earthed electrode in the form of mesh would neverbe thickly covered with carrier liquid. Further, the electrode in suchform would ensure electrical neutralization of charged mist to proceedat an appropriate speed, thereby eliminating the above-described danger.FIG. 4 shows an example of the earthcd electrode in the form of mesh.

By making the earthed electrodes in such mesh form, exhaust of thehygienically deleterious carrier vapor can be prevented substantiallycompletely and the recovered carrier liquid can be reused, and thisleads to the provision of a recovery device which is highly economicaland highly safe. Substantially all (90% or more) of the mist in the airA2 is removed by the mist collector described above, while the slightamount of remaining mist is completely removed by a simple filter 27such as wire netting or the like, and thus the air A2 now containingonly a slight amount of carrier vapor (saturated vapor at roomtemperature) is returned to the fixing-drying chamber by the blower 16for reuse.

The carrier liquefied by the heat-exchange condenser 14 and mistcollector 15 may be collected through a discharge port 27 into a tank28, from which the carrier liquid is returned to a developing device forreuse.

On the other hand, an air flow A3 divided from the air flow A3 at theduct 17 is further cooled down in the cooling chamber 18 to an extremeextent so that substantially all of the carrier vapor in such air flowis liquefied, and then exhausted into the atmosphere. This exhaust air,indicated by A5, is of small amount and substantially clean, thus beingnever deleterious hygienically. The amount of carrier liquid resultingfrom the condensation in the cooling chamber 18 is collected in a tank29, but the carrier liquid so collected in this tank 29 carries with itsome water content of the air resulting from the condensation effectedin the cooling chamber and cannot directly be reused. It must beregenerated before reused.

The carrier liquid used with the electrophotographic copying machine ofthe liquid development type is petroleum solvent generally known by thetradename of lsopar whose main component is isoparafine which isinitially low in unsaturation degree and odorless. However, when thecarrier liquid has been heated and vaporized in the fixing station afterdevelopment or after image transfer and thereafter the carrier liquidhas been recovered with the isoparafine vapor cooled and condensed, thepolymerization chain of hydrocarbon is cut off under the influence ofthermal cracking or the like to increase the unsaturation degree ofisoparafine, as is well known. Moreover, the carrier liquid so recoveredmight further contain other ingredients resulting from the thermalcracking of the constiuents forming the copy medium and thermal crackingof the constituents forming the developing liquid, and it is believedthat the odor emitted from the recovered carrier liquid is attributableto the combination of those various ingredients, although the true causehas not yet been discovered definitely.

Nevertheless, the investigations into the method of deodorizing andpurifying the recovered carrier liquid have shown that the unpleasantodor noted above can be almost completely removed by passing the carrierliquid through an adsorbent such as active carbon, silica gel, activealumina, active magnesium, acid clay, bentonite, diatomite, calciumcarbonate, titanium oxide or the like.

The present invention enables the repeated use of the recovered carrierliquid by employing one of the above-ennumerated adsorbents as theadsorbent indicated at A in FIG. 1 so that the carrier liquid resultingfrom the action of the heabexchange condenser and mist collector maypass through the adsorbent A.

Thus, the carrier liquid recovered in the abovedescribed manner isdeodorized and safely available for reuse.

FIG. 5 shows the details of the tank 28. The tank 28 for recovering thecarrier vapor produced from the developing liquid and storing the thusrecovered liquid includes a first partition wall 28 and a secondpartition wall 28 which serves to separate the recovered liquid until itreaches a predetermined liquid level. In the first chamber (right-handside), the carrier liquid recovered by the recovery device is mixed withwater and other impurities and the mixture drips into the tank 28through the inlet 27. The first partition wall 28, serves to prevent themixture of carrier liquid and water from running directly over thesurface of the recovered liquid to go beyond the second partition wall,and for this purpose the lower end 28 of the partition wall is at alower level than at least the upper end 28 of the second partition wall.The mixture of carrier liquid and water is first stored in the firstchamber, where with lapse of time the mixture is completely separatedinto an upper layer of carrier liquid 41 and a lower layer of water 42due to the difference in specific gravity (for example, if the carrierliquid is lsopar H, the ratio of specific gravity between the lsopar Hand water is 0.75 I). As is already apparent, the carrier liquid formingthe developer must be insulative and should not be mixed with water. Itis for this reason that the carrier liquid and water are completelyseparated from each other in the first chamber, and thereafter when theliquid level exceeds a predetermined level, only the lsopar H liquidforming the upper layer is caused to overflow the top 28 of the secondpartition wall 28 for collection in the second chamber (left-hand side).The carrier liquid so collected in the second chamber is delivered by apump 31 driven from a motor 29 through the rotary shaft 30 thereof so asto be returned through a pipe 32 into a developer tank D which is thedeveloper storage container of the developing means, thus becoming readyfor reuse. In this case, however, carrier liquid contains no developerand therefore, it is necessary to add a suitably concentrated developerto the stored liquid and control the density of the developing liquid bymeans of toner density regulator or the like.

Within the recovered liquid tank 28 of the described construction,liquid level detector means is further provided in each of the first andsecond chambers. Especially, the water recovered and stored in the firstchamber must not overflow the second partition wall 28 and for thisreason, it is necessary to detect the liquid level of the lower layerwhen it exceeds a predetermined level and to remove the excess liquid.In FIG. 5, such detector means is designed to detect the level with theaid of the difference between the dielectric constant of carrier liquidand that of water, and comprises two conductive plates closely spacedand opposed to each other to detect the variation in inductioncoefficient therebetween. This circuit is shown in FIG. 7. When thewater of the lower layer exceeds a predetermined level, an electricalsignal is produced to open an electromagnetic valve V1 for apredetermined time to permit the water to fall into a tank 36 locatedbelow the tank 28. The electromagnetic valve V1 remains open until thewater 42 sufficiently flows down, whereafter the valve is again closedto store the recovered liquid in the tank 28. In the second chamber,there is provided level detector means for controlling the liquid levelwithin a predetermined range, and this level detector means includes afloat 33, an actuator 34 actuated by the float 33, and microswitches M81and M82 actuated by the actuator 34. Microswitch MSl detects the upperlimit of the liquid level and microswitch MS2 detects the lower limit ofthe liquid level. The operating circuit is shown in FIG. 8. As shownthere, M52 is a normally closed switch. When the float 33 rises toactuate the actuator 34 out of engagement from the microswitch M52, themicroswitch M82 is closed. When the liquid level further rises to closethe microswitch MSl, a relay RL-A is energized whose contact -1 is thusclosed to energize the motor 29, which in turn drives the pump 31 topump up the carrier liquid into the de veloping tank D. If thiscondition remains unchanged, the microswitch MSl would immediately beopened to substantially prevent the carrier liquid 41 from being pumpedup. To avoid this, the relay RL-A is held by its contact a-Z to maintainthe motor energized irrespective of the opening of the switch MSl, andthe motor M is not deenergized until the lower itself detectormicroswitch M82 is opened, whereupon the pumping operation is stopped.

FIG. 6 shows liquid level detector means for detecting the liquid levelof the lower layer within the first chamber by using a float 40 and amicroswitch MS3. This utilizes the difference in specific gravitybetween the two liquid layers (0.75 l) and the float 40 is disposed inthe interface between the two layers. When the float 40 exceeds apredetermined level, it actuates the switch M83 to open theelectromagnetic valve V], thus permitting the liquid of the lower layerto fall into the underlying tank 36.

Further, in this embodiment, the developing tank D is provided with aliquid level detector microswitch M54, a float 37 and an actuator 38. Agreat deal of carrier liquid (lsopar H) is prestored in the secondchamber 28, and the carrier liquid (lsopar H) recovered by the recoverydevice is caused to overflow the first chamber to mix with thepre-stored carrier liquid in the second chamber. By the operation of theliquid level detector means of the developing tank D, the pump 31 isoperated to supply the carrier liquid from the second chamber to thedeveloping tank. The liquid pre-stored in the second chamber is notlimited to carrier liquid but it may be developer with which therecovered carrier liquid may be mixed, and such mixture may becirculated to the developing device.

The electric circuit of FIG, 7 will now be explained. It includes a basetuning type oscillator circuit 1, a voltage doubling detector circuit 2,and a detection output amplifier circuit and thyristor trigger circuit 3which varies the tuning frequency of the detector circuit in accordancewith the variation in the capacitance of a capacitor Cx. The capacitanceof the capacitor Cx is greater when the space between electrodes of thecapacitor is filled with water than when such space is filled with airor lsopar, thus reducing the tuning fre quency. The output voltage ofthe detector circuit can be higher as the turning frequency f, is closerto the frequency f, of the oscillator circuit, and this may be utilizedto detect the level. More specifically, if the oscillation frequency inthe dotted frame 1 is f,;, the tuning frequency f, of T is in therelation that f, f with the capacitor Cx filled with water and theoutput voltages Bi and Er are regulated by a variable resistor VR tosatisfy the relation Ei Er, and the output voltage E0 is produced in theamplifier A, This is regulated so as to assume a sufficient value totrigger the thyristor SCR. When the thyristor SCR is triggered, theelement K is energized to close the contact K1 and K2 and therebyenergize the motor M while the microswitch M82 is closed and the valveoperating solenoid SL is also energized to open the valve. As the motorM is rotated to cause the cam-l to actuate and open the microswitch MS],the thyristor SCR is turned off to deenergize the element K and open thecontacts K1 and K2, thus deenergizing the solenoid SL and closing thevalve. Irrespective of the opening of the contact K1, the motor Mcontinues its rotation because the microswitch M82 is closed, but whenthe cam-2 actuates the switch MSZ, this switch is opened to deenergizethe motor M in preparation for a subsequent operation.

The above-described construction of the present invention results in theadvantages described below,

Exhaust of the hygienically deleterious carrier vapor into theatmosphere is substantially completely avoided and this ensures safetyduring a mass production of COPIES.

The recovered carrier liquid is available for reuse, which is a greateconomical advantage.

Since most of the air used for the fixing-drying process is cyclicallyused, the rate of recovery of the carrier is higher than when suchcyclical use of the air is not adopted, and the heat-exchange condenser14 need not be of so great a capacity. Also, the air A5 exhausted intothe atmosphere is so small in amount that the cooler 18 may be of smallcapacity.

Since the heat-exchange condenser 14 is of the flat type and the mistcollector 15 is of the corona discharge type, the flow path resistanceis much less than in a filter type collector using steel, wool or likematerial and thus, the blower in the flow path may be of small size.

The air A3 once used to recover the carrier is heated in theheat-exchanger l4, and then used for the fixingdrying process toexpedite such process, which means a thermal economy.

Further, the liquid containing carrier vapor from the developing stationand from the fixing station can be recovered in the tank having thefirst and second partition walls and can be separated into carrierliquid and water due to their difference in specific gravity, whereafterthe carrier liquid so separated can be returned to the developing tankfor reuse. This leads to the provision of a highly economical devicewhich permits reuse of the developing liquid.

We claim:

1. A developing liquid recovery device comprising:

a drying chamber which includes an inlet and an outlet for a copy mediumand which is of substantially hermetically sealed construction, saiddrying chamber accommodating heating means for heating the copy mediumbearing an image formed by wet-developing to dry the copy medium withdeveloping liquid vapor produced from the copy medium;

a condenser chamber for accommodating means for cooling the developingliquid vapor produced in said drying chamber to form the vapor intomist;

a mist collector chamber for accommodating means for applying anelectric field to the developing liquid vapor in the form of mist tocollect the mist;

means for circulating an air flow through said drying chamber, saidcondenser chamber and said mist collector chamber in the order named;and

discharging means disposed downstream of said mist collector chamber andupstream of said drying chamber, said discharging means discharging apart of the air flow to maintain the pressure in said drying chamber ata lower value than that of the ambient pressure.

2. A developing liquid recovery device according to claim 1, whereinsaid electric field applying means includes a corona discharger forcharging the mist of the developing liquid.

3. A developing liquid recovery device according to claim 1, whereinsaid electric field applying means includes at least a couple ofelectrode plates for forming an electric field.

4. A developing liquid recovery device according to claim 1, wherein thedeveloping liquid liquefied in said mist collector chamber is led todeveloper means to use the developing liquid repeatedly.

5. A developing liquid recovery device according to claim 1, wherein theair has passed through said mist collector chamber is used for thecooling means of said condenser chamber.

6. A developing liquid recovery device comprising:

a drying chamber whhich includes an inlet and an outlet for a copymedium and which is of substantially hermetically sealed construction,said drying chamber accommodating heating means for heating the copymedium bearing an image formed by wet-developing to dry the copy mediumwith developing liquid vapor produced from the copy medium;

a condenser chamber for accommodating means for cooling the developingliquid vapor produced in said drying chamber to form the vapor intomist;

a mist collector chamber for accommodating means for applying anelectric field to the developing liquid vapor in the form of mist tocollect the mist;

absorbing means for passing through an absorbent the developing liquidcollected by said mist collector to purify the developing liquid;

means for circulating an air flow through said drying chamber, saidcondenser chamber and said mist collector chamber, in the order named;and

discharging means disposed downstream of said mist collector chamber andupstream of said drying chamber. said discharging means discharging apart of the air flow to maintain the pressure in said drying chamber ata lower value than that of the ambient pressure.

7. A developing liquid recovery device according to claim 6, whereinsaid absorbent includes at least one of the group consisting of activecarbon, silica gel, active alumina, active magnesium, acid clay,bentonite, diatomite, calcium carbonate and titanium oxide.

8. A developing liquid recovery device according to claim 6, wherein thedeveloping liquid liquefied in said mist collector chamber is led todeveloper means to use the developing liquid repeatedly.

9. A developing liquid recovery device comprising:

a drying chamber which includes an inlet and an outlet for a copy mediumand which is of substantially hermetically sealed construction, saiddrying chamber accommodating heating means for heating the copy mediumbearing an image formed by wet-developing to dry the copy medium withdeveloping liquid vapor produced from the copy medium;

a condenser chamber for accommodating means for cooling the developingliquid vapor produced in said drying chamber to form the vapor intomist;

a mist collector chamber for accommodating means for applying anelectric field to the developing liquid vapor in the form of mist tocollect the mist;

a filter for further collecting the mist from an air flow which haspassed through said mist collector chamber;

means for circulating the air flow through said drying chamber, saidcondenser chamber, said mist collector chamber and said filter, in theorder named; and

discharging means disposed downstream of said filter and upstream ofsaid drying chamber, said discharging means discharging a part of theair flow to maintain the pressure in said drying chamber at lower valuethan that of the ambient pressure.

10. A developing liquid recovery device according to claim 9, whereinsaid filter includes a net of metal.

11. A developing liquid recovery device according to claim 9, wherein atleast one of, the developing liquid liquefied in said mist collector,the developing liquid collected by said filter, is led to a developermeans to use the developing liquid repeatedly.

12. A developing liquid recovery device according to claim 9, whereinthe air which has passed through said filter is used for the coolingmeans of said condenser chamber.

1. A developing liquid recovery device comprising: a drying chamber which includes an inlet and an outlet for a copy medium and which is of substantially hermetically sealed construction, said drying chamber accommodating heating means for heating the copy medium bearing an image formed by wetdeveloping to dry the copy medium with developing liquid vapor produced from the copy medium; a condenser chamber for accommodating means for cooling the developing liquid vapor produced in said drying chamber to form the vapor into mist; a mist collector chamber for accommodating means for applying an electric field to the developing liquid vapor in the form of mist to collect the mist; means for circulating an air flow through said drying chamber, said condenser chamber and said mist collector chamber in the order named; and discharging means disposed downstream of said mist collector chamber and upstream of said drying chamber, said discharging means discharging a part of the air flow to maintain the pressure in said drying chamber at a lower value than that of the ambient pressure.
 2. A developing liquid recovery device according to claim 1, wherein said electric field applying means includes a corona discharger for charging the mist of the developing liquid.
 3. A developing liquid recovery device according to claim 1, wherein said electric field applying means includes at least a couple of electrode plates for forming an electric field.
 4. A developing liquid recovery device according to claim 1, wherein the developing liquid liquefied in said mist collector chamber is led to developer means to use the developing liquid repeatedly.
 5. A developing liquid recovery device according to claim 1, wherein the air has passed through said mist collector chamber is used for the cooling means of said condenser chamber.
 6. A developing liquid recovery device comprising: a drying chamber whhich includes an inlet and an outlet for a copy medium and which is of substantially hermetically sealed construction, said drying chamber accommodating heating means for heating the copy medium bearing an image formed by wet-developing to dry the copy medium with developing liquid vapor produced from the copy medium; a condenser chamber for accommodating means for cooling the developing liquid vapor produced in said drying chamber to form the vapor into mist; a mist collector chamber for accommodating means for applying an electric field to the developing liquid vapor in the form of mist to collect the mist; absorbing means for passing through an absorbent the developing liquid collected by said mist collector to purify the developing liquid; means for circulating an air flow through said drying chamber, said condenser chamber and said mist collector chamber, in the order named; and discharging means disposed downstream of said mist collector chamber and upstream of said drying chamber, said discHarging means discharging a part of the air flow to maintain the pressure in said drying chamber at a lower value than that of the ambient pressure.
 7. A developing liquid recovery device according to claim 6, wherein said absorbent includes at least one of the group consisting of active carbon, silica gel, active alumina, active magnesium, acid clay, bentonite, diatomite, calcium carbonate and titanium oxide.
 8. A developing liquid recovery device according to claim 6, wherein the developing liquid liquefied in said mist collector chamber is led to developer means to use the developing liquid repeatedly.
 9. A developing liquid recovery device comprising: a drying chamber which includes an inlet and an outlet for a copy medium and which is of substantially hermetically sealed construction, said drying chamber accommodating heating means for heating the copy medium bearing an image formed by wet-developing to dry the copy medium with developing liquid vapor produced from the copy medium; a condenser chamber for accommodating means for cooling the developing liquid vapor produced in said drying chamber to form the vapor into mist; a mist collector chamber for accommodating means for applying an electric field to the developing liquid vapor in the form of mist to collect the mist; a filter for further collecting the mist from an air flow which has passed through said mist collector chamber; means for circulating the air flow through said drying chamber, said condenser chamber, said mist collector chamber and said filter, in the order named; and discharging means disposed downstream of said filter and upstream of said drying chamber, said discharging means discharging a part of the air flow to maintain the pressure in said drying chamber at lower value than that of the ambient pressure.
 10. A developing liquid recovery device according to claim 9, wherein said filter includes a net of metal.
 11. A developing liquid recovery device according to claim 9, wherein at least one of, the developing liquid liquefied in said mist collector, the developing liquid collected by said filter, is led to a developer means to use the developing liquid repeatedly.
 12. A developing liquid recovery device according to claim 9, wherein the air which has passed through said filter is used for the cooling means of said condenser chamber. 